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S is for Stabilization

Using Adobe After Effects to fix strobing time-lapse footage By Stephen Schleicher
Last time I discussed a way to capture time-lapse footage using a digital still camera for use in your digital masterpiece. This time Ill discuss how to fix a problem that can arise in time-lapse footage.

One of the drawbacks to capturing time-lapse footage is the exposure may change from minute to minute causing a flicker or strobe effect in the completed project. For outdoor time-lapse video, this is usually due to clouds passing over the sun, which casts a shadow over the subject area. Depending on the frame rate of this can be very annoying to the viewer.

To solve this problem, begin by loading the still images into Adobe After Effects as an image sequence and create a composition of the same length.

In the timeline find a frame that you will use as the reference for all other frames.

Reference Frame
It is important to find a frame that will represent the correct exposure for the entire clip

From the Effects palette, choose Color Stabilizer, and apply it to the time-lapse layer. (Incidentally, this same technique can be used to stabilize black and white archive footage from years and years ago.)

The Color Stabilizer effect is essentially a way of adjusting levels, curves, or brightness on a frame-by-frame basis without having to set a bazillion keyframes.

In the Effects Control Panel, select the type of stabilization you will be performing. Here at the DMN Central Division, we dont have too many days where white puffy clouds are going to be constantly moving in and out of the sun - it is either sunny or cloudy, so for this exercise I am going to be dealing with brightness levels only.

Depending on what method you choose, you will notice that you are able to set a black reference point (brightness), black and white reference points (levels), or black, white and mid points (curves). Since I am using brightness for this example, I only have to set a black reference point.

Click on the black point crosshair and move the selection area to the area of the image that is supposed to be pure black. In the image below, the bench with the black legs would be the best choice. If you want the image to be even darker, select another appropriate area. I decided I wanted the shadow on the sidewalk to be pure black, so I moved the reference point to that region.

Setting the reference point
Find the area of the image that you want to represent pure black and move the selection region there. In this example, I selected the shadow region.

The Sample Size determines the radius (in pixels) that Adobe After Effects will be using to sample the image area.

Once you have your reference points in place, click on Set Frame to specify the current frame as the reference frame. Now After Effects will adjust the total exposure for all other frames in the timeline to remove unwanted flicker, strobing, color variations, etc.

Click on images to view the before and after results of using the Color Stabilizer effect.

Color Stabilization Off
Click image to view QuickTime movie of time-lapse with Color Stabilization off.

Click image to view QuickTime movie of time-lapse with Color Stabilization on.

When not working deep in the labs of the DMN Central Division testing the latest and greatest software/hardware products Stephen Schleicher can be found at the local university teaching a few courses on video and web production. He can be reached at schleicher@mindspring.com. You can also visit him on the web at www.mindspring.com/~schleicher

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Stephen Schleicher is a well known writer, visual effects artist and media guru! You can see more of Stephen at
www.majorspoilers.com and www.stephenschleicher.com
Related Keywords:Adobe After Effects, Stephen Schleicher, time-lapse, effect, color stabilizer, stabilization, tutorial

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